High tension fuse



July 22, 1941. K. DANNENBERG 2,249,945

HIGH TENSION FUSE .Fil-9d Feb. 24, 1939 and n.

Attorney I Patented July 22, 1941 UNETED STATES PATENT GFFCE ApplicationFebruary 24, 1939, Serial No. 258,274 In Great Britain February 24, 1938Claims.

This invention has reference to high tension fuses having one or morefusible elements mounted on a support.

The primary object of the invention is to ensure good thermal insulationbetween the turns of the fusible element whilst making the fuse nolonger or even shorter than existing fuses of the same current rating.

A further object of the invention is to decrease the length of fuses ofhigh current ratings in order to give the fuses the same length as fusesof small current ratings at the same voltage in cases where the fusibleelement extends from end to end of the fuse.

Another object of the invention is to make the construction of highvoltage powder filled cartridge fuses possible with low current ratingsfor instance under two amperes when the fusible elements extend from endto end of the fuse and at least two of the elements are of differentspecific resistance, a difficulty in connection with the construction ofhigh voltage, low current capacity fuses being caused by the neness ofthe elements.

According to the present invention the fusible element comprises anumber of wires or metal strips wound around the outer peripheries oftwo or more nested supports having ribs or projections on theirperipheries making line or point contact with the tightly applied wiresor strips. Owing, therefore, to the invention the spacing between theconvolutions may be as great as desired to give the necessary degree ofthermal insulation, the greater the spacing the more numerous the nestedsupports in order to accommodate the requisite number of elements.Further, the length of the sum of the supports is such as to enableelements extending along the length of the fuse and of high currentratings to be accommodated in a fuse having the same length as one cfsmall current rating, the rated voltage being the same in each case. Inaddition to these advantages it is possible to provide a fuse of lowcurrent capacity with a very fine wire of higher specific resistancethan another or other wires or strips in the fuse because, the ne wire,being tightly wound around the outer periphery of the innermost support,is supported at a large number of spaced points.

It will be understood that the fusible element may be embedded in powderaccording to my copending patent application Serial No. 162,789.

The invention will now be described with reference to the accompanyingdrawing wherein:

Fig. 1 is a side elevation, partly in section, of one form of atwo-support fuse; and

Fig. 2 is a side elevation of one end of a support with a fusibleelement of strip-like form applied to it.

In Fig. 1 a hollow support I of refractory insulating material is nestedwithin a hollow support 2' of like material, both supports beinglongitudinally ribbed as described in my co-pending patent applicationSerial No. 162,739. The length of the support I is less than that of thesupport 2 so that the ends of I lie within the ends of 2 and the overalldiameter of the said support I is less than the diameter of the bore ofthe support 2 to provide a space 3 between the supports. Contact sleeves4 and 5 are fitted to the ends of the supports I and 2 so as to projectfrom the said ends and, thereby, to provide sockets. Hollow steppedbushes as 6 are pushed into the said sockets and secure the saidsupports together whilst centering I within 2. Asbestos Washers 1 arelocated between the tread portions of the stepped bushes and the ends ofthe supports. Fusible elements 8 in the form of strips, for example,silver strips, are wound round the supports and connected to the sleeves4 and 5, the contact between the supports and the strips being linecontact owing to the ribs, and a central fusible element 9 of higherspecific resistance than the strips 8, for example, tungsten, and in theform of a longitudinal coil is arranged within the hollow of the supportI, the ends of the coil being electrically connected to the steppedbush.

The unit comprising the parts I to 9 is located within a sheath I0 ofrefractory, insulating material, the bore of the sheath being greaterthan the overall diameter of the support 2 to provide a space II.Contact sleeves I2 are cemented to the sheath at the ends thereof andeach has an inwardly turned flange I3 at its outer end. A number ofscrew-threaded studs as I4 project from each flange I3 parallel to theaxis of the sheath. The studs receive the flange of a hollow, flangedbush I5 which is a push fit in the hollow of the stepped bush 6, and thesaid flange is clamped between I3 and two clamping rings I E held inposition by nuts on the studs. An asbestos washer I1 is located betweeneach fiange I3 and the corresponding end of the sheath I0. Thus, thebush I5 centres the unit previously referred to within the sheath Il).

Tread portions of each bush as 6 and the flange of each bush I5 haveVentilating holes I8. The fusible elements 8 and 9 are embedded inpowder preferably according to my cci-pending patent application SerialNo. 162,789 and metal foil, not shown, seals the ends of the fuse so asto prevent powder unintentionally escaping from the fuse. The metal foilis preferably clamped between the two rings IS. The metal foil providesan outlet for gases in the event of excessive pressure being producedwithin the fuse.

Owing' to the construction and arrangement of the bushes a unitcomprising the parts l to 9 can be easily removed from the sheath andreplaced, or replaced by a similar unit.

The temperature of the fusible elements of high tension fuses at, say,300 amperes rating is usually about 250 to 309 C. with the result thatthe solder used for connecting the fusible elements to their contacts ismelted or dangerously overheated. In order to overcome this diiculty Iconnect the fusible strips 8 to their contact sleeves in a manner whichwe will now describe with reference, more particularly, to Fig. 2 of theaccompanying drawing.l The strips 8 are pinched at two points at eachend between the longitudinal ribs 2G on the support (as I or 2, Fig. 1)and binding wires 2l, 22. An end of each strip is soldered at 23 to thewires 22, said wires being further than the wires 2l from the sleeve (4or 5, Fig, l) and both sets of binding wires are electrically connectedto the sleeve by conducting fingers 1t will thus be seen that thesoldered points between the strips and the binding wires E?. are notdirectly in the electrical circuit of the strips so the heating to whichthe soldering is subjected is reduced to about the operating temperatureof the refractory supports, namely, about 160 to 120 C.

It will be understood that when a fuse is provided with more than twonested supports the steps of the stepped hush as E Yare increased innumber correspondingly and the hollow of the outermost step receives theflanged bush, the lengths of the said supports decreasing from the outersupport to the innermost support in order to accommodate the steps. Anoccasion when more than two supports would be employed is when thedegree of iineness of the element such as 9 is such that it cannotsatisfactorily be stretched from end to end of the hollow of the supportas I, the said wire in this event being wound around a. longitudinallyribbed support.

What I claim is:

1. A high tension fuse unit comprising a number of nested supports ofrefractory, insulating material, ribs or projections on the peripheriesof said nested supports and fusible elements tightly wound round saidsupports to make line or point contact at said ribs or projections, thesupports providing separate independent compartments closed one againstthe other whereby the dissipation processes occuring when the fusefunctions cannot interfere with each other.

2. A high tension fuse unit according to claim 1, comprising contactsockets at the ends of the supports, a co-axially stepped bush at oneend of the unit engaging with the sockets at this end and. a secondco-axially stepped bush at the other end of the unit engaging with thesockets thereat, each of said bushes connecting the sockets with whichit is in engagement in electrically parallel manner and the bushesholding said supports cc-axially with respect to each other.

3. A high tension fuse unit according to claim 1, comprising pairs ofmetal binders arranged one pair at one end of a support, another pair atthe other end thereof, a third pair at the end of another support, andso on, each tail of each element being united with the inner binder ofthe corresponding pair and the binders being electrically connected tocontact elements at the corresponding ends of their supports.

4. A high tension fuse unit as defined in claim 1 wherein one of thefusible elements is arranged co-axially of the innermost support andwherein the other of the fuse elements is arranged circumferentially ofthe other support, the respective fuse elements being electricallyconnected at their ends.

5. A construction as dened in claim 1 wherein one of the supports isformed with longitudinally extending ribs and wherein the fuse elementis tightly wrapped around said support for contact with the ribs, andfree of contact between the ribs, whereby a considerable space isprovided between the various points of support of the fuse element toprevent metallization of the intermediate space between said points.

KURT DANNENBERG.

